1. Technical Field
The present invention relates to an insulated state detection device which is usable in a state of being mounted on a vehicle.
2. Background Art
For example, in a vehicle using electric power as propulsion energy, such as an electric vehicle, a DC power supply device that outputs a high voltage of about 200 V may be mounted. The vehicle equipped with such a high-voltage DC power supply device is used in a state where positive and negative power lines of the DC power supply device and a vehicle body are electrically insulated from each other. In other words, the vehicle body is not used as an earth of a power supply that outputs a high voltage.
In such a vehicle, there is a need to check and confirm that wirings of the output of a high-voltage DC power supply and the vehicle body are well electrically insulated from each other in order to secure safety or the like. Conventional insulated state detection devices used in performing such a checking are disclosed in JP-A-2004-170146, JP-A-2008-089323 and JP-A-2008-309751 for example.
Such an insulated state detection device uses a flying capacitor. A detection capacitor (referred to as “flying capacitor”) is connected, only for a certain period of time, between high-voltage positive and negative power lines and a ground electrode (vehicle body) via a switching element. A ground fault resistance, i.e., an insulation resistance between the power lines and the ground electrode is calculated by monitoring the charging voltage of the flying capacitor and performing calculation based on the charging voltage.
Further, JP-A-2004-170146 and JP-A-2008-089323 disclose a technique related to fault detection of a switch for switching the flying capacitor.
Further, JP-A-2008-309751 discloses a technique for protecting a circuit in such a way that a high voltage greater than a predetermined level is not applied to a circuit for detecting a voltage of the flying capacitor.
However, in a vehicle equipped with a DC power supply device that outputs a high voltage, it may be desirable to check, not only at shipment of a vehicle or periodic inspection but also frequently on a daily basis, that wirings of the output of a high-voltage DC power supply and a vehicle body are well electrically insulated from each other.
In such a case, it is necessary to equip the insulated state detection device on a vehicle as a sensor, as described above. When a vehicle is equipped with the insulated state detection device as a sensor, it is possible to identify the presence or absence of the occurrence of abnormality by regularly measuring a ground fault resistance (insulation resistance), e.g. during use of the vehicle using the insulated state detection device.
Actually, it is necessary that the insulated state detection device measures voltage of the flying capacitor while controlling ON/Off of each switching element in accordance with a predetermined schedule and calculates the ground fault resistance based on the measured voltage and a calculation formula. Further, in order to identify the presence or absence of a failure of each of switching elements incorporated in the insulated state detection device or to improve reliability of the measured ground fault resistance value, a control of stopping measurement at the timing that is not suitable for the measurement is also required. Such a complicated control is executed by a control circuit such as a microcomputer incorporated in the insulated state detection device.
Meanwhile, an actual vehicle is equipped with various electronic control units (ECU) in order to make a predetermined diagnosis on the function of each pail of the vehicle and to display the diagnosis result or to reflect the diagnosis result to other controls. Accordingly when the insulated state detection device is equipped on a vehicle as a sensor, the insulated state detection device is connected under the electronic control unit (ECU) that comes standard with a vehicle side. In that case, a host electronic control unit (ECU) acquires a ground fault resistance value (that is a measurement result), as necessary, from the ECU-affiliated insulated state detection device through communication and outputs the final diagnosis result by making a diagnosis of such information.
Meanwhile, in an actual vehicle, there is a possibility that an environment in which the insulated state detection device measures the ground fault resistance changes in various ways. For example, the ground fault resistance to be detected also changes when power supply voltage changes in accordance with charge/discharge of a vehicle battery. Further, a possibility is considered that tire ground fault resistance is temporarily decreased when each of on-vehicle devices is operated, for example. Further, a possibility is also considered that the ground fault resistance temporarily changes with the changes in the weather (such as rainfall, for example) or changes in temperature or humidity, etc.
Since the electronic control unit (ECU) that comes standard with a vehicle is able to make a final diagnosis, based on various information that can be acquired on the vehicle, it is possible to output a reliable diagnosis result for the ground fault resistance.
However, despite the fact that the insulated state detection device as described above performs measurement and calculation at independent timing that is established by its own, the host electronic control unit (ECU) can receive only the data of ground fault resistance of the measurement results.
For example, in a case where the insulated state detection device measures the grounding and then recognizes that the situation is nest suitable for measurement, there is a possibility that the insulated state detection device stops measuring and transmits data of ground fault resistance measured in the last to the host electronic control unit. Accordingly, the host electronic control unit cannot discriminate whether the data of ground fault resistance received from the ECU-affiliated insulated state detection device is the latest measurement data or an old measurement data. Specifically, the host electronic control unit cannot grasp whether or not the data of ground fault, resistance received from the ECU-affiliated insulated state detection device is a data of ground fault resistance measured at timing that is intended by its own (the electronic control device) when making a diagnosis on the data of ground fault resistance received from the ECU-affiliated insulated state detection device. Accordingly, there is a possibility that error in diagnosis occurs. For example, despite the fact that the data received from the insulated state detection device is an old data measured at timing in which the host electronic control unit considers the measurement to be invalid, there is a possibility that the data received from the insulated state detection device is considered as the reliable latest data and therefore a diagnosis is made.
Accordingly, it is considered that information representing the time in which the ground fault resistance is measured, for example, is transmitted from the insulated state detection device to the host electronic control unit. However, in order to handle information of time (hours, minutes, seconds, etc.), the number of bits more than that of the ground fault resistance is required and therefore waste is increased. Furthermore, it is not possible to grasp the correct time, unless the time of the insulated state detection device side and the time of the host electronic control device side are synchronized with each other in some ways.
The present invention has been made in consideration of the above situations and an object thereof is to provide an insulated state detection device capable of transmitting information that is helpful to allow a host electronic control unit performing a final diagnosis to grasp actual measurement timing of a ground fault resistance data.